If you’ve driven along a highway in Ontario recently, you’ve likely seen tall, dense stands of reeds dominating ditches and wetlands. These plants are invasive phragmites (Phragmites australis subspecies australis), and they’ve become one of the most serious ecological threats in the province.
Once established, phragmites crowd out native species, reduce biodiversity, and alter wetland ecosystems. The Government of Ontario and environmental organizations consider them the province’s worst invasive species, and controlling their spread has become a top conservation priority.
This article explains what phragmites are, why they’re such a problem in Ontario, and what steps are being taken to fight them.
What Are Phragmites?
Phragmites are tall, perennial grasses that grow in wetlands and along shorelines. While a native subspecies of phragmites does exist in Ontario, it is non-aggressive and part of the natural wetland ecosystem. The problem lies with the invasive subspecies, which arrived from Eurasia in the 1800s and has spread aggressively across North America.
Key features of invasive phragmites:
- Height: Grows up to 5 metres tall, much larger than the native subspecies.
- Stems: Densely packed, often more than 200 stems per square metre.
- Seed heads: Dense, tan-coloured plumes at the top of each stalk.
- Roots: Deep, extensive rhizome systems that allow rapid spread.
Unlike the native phragmites, invasive stands form thick monocultures that choke out virtually all other plants and wildlife.
Why Are They a Problem in Ontario?
Invasive phragmites are more than just tall grasses. They actively alter the environment in ways that harm Ontario’s wetlands, wildlife, and even people.
- Loss of biodiversity
- Native wetland plants such as cattails, sedges, and wildflowers are quickly displaced.
- This eliminates food and habitat for waterfowl, turtles, amphibians, and pollinators.
- Altered wetland hydrology
- Dense root mats block water flow, changing how wetlands function.
- This can increase flooding in some areas while drying out others.
- Increased fire risk
- Dead stalks accumulate each year, creating thick mats of dry material that are highly flammable.
- Reduced recreational and aesthetic value
- Phragmites spread into beaches, ditches, and trails, making natural areas less accessible and less appealing.
- Economic costs
- Managing phragmites is expensive for municipalities and conservation authorities, with millions spent annually on removal and control efforts.
How Did They Spread?
The invasive subspecies spreads through both seeds and its extensive rhizome network. Rhizomes can grow several metres per year, producing new shoots that quickly expand colonies. Seeds are easily transported by wind, water, animals, and human activity.
Disturbed areas, such as road construction sites or drainage ditches, are particularly vulnerable to new infestations. Once established, phragmites are extremely difficult to remove.
Identifying Invasive Phragmites
Distinguishing invasive phragmites from the native subspecies can be tricky, but a few traits stand out:
- Invasive phragmites: Tall (up to 5 m), dense stands, dark green leaves, large tan plumes, stems often red at the base.
- Native phragmites: Shorter (under 2 m), more scattered growth, lighter green leaves, smaller seed heads.
For photos and identification help, the Nature Conservancy of Canada provides useful resources: Fighting Phragmites in Ontario
